The introduction of 16:9 aspect ratio picture tubes requires a method to adapt the display width and height to the format of the picture to be displayed. In particular, when a 4:3 aspect ratio picture is displayed on a 16:9 picture tube, the display width must be reduced. This may be achieved by appropriate digital video signal processing or simply by reducing the deflection current amplitude. A reduction of horizontal scan width obviates the requirement to digital process (shrink) the 4:3 aspect ratio signal prior to display with a 16:9 aspect ratio tube.
The inventive arrangements described herein teach a switching arrangement which reduces the horizontal scan width by 25%, this being the reduction required to permit the display of a 4:3 aspect ratio video source, without geometrical distortion, on a 16:9 video display.
The circuit takes advantage of a raster corrected horizontal deflection circuit with grounded yoke. This circuit arrangement provides a low cost solution in which a single transistor switch controls all deflection parameters, for example deflection current amplitude, retrace time, raster correction and "S" shaping.